CLAPAREDE, ON TREMA'TODA, ETC. 93 
main trunks or in the course of the vibrating vessels. Occa- 
sionally, individuals may be noticed presenting no corpuscles, 
which may be owing to the circumstance either that they 
were never formed, or that they had been discharged. The 
oviform enlargements of the vessels, however, always exist. 
Having made this observation, I had the pleasure of satis- 
fying Johan. Miiller, Dr. De la Valette, Professors Weinland 
and Lachmann of its correctness ; and more recently I have 
had the satisfaction of showing the connexion between the 
calcareous corpuscles and the excretory system to Professor 
Virchow. 
Dr. De la Valette thinks he has observed minute twigs 
given off from the oviform sacs, but of this I have been 
unable to satisfy myself. 
In Diplostomum rachieum it is so easy to perceive that the 
calcareous corpuscles are situated within the excretory sys- 
tem, that it is surprising this relation has not been earlier 
noticed; but its occurrence in this case having been esta- 
blished, it naturally suggested itself to suppose that a similar 
condition was not limited to D. rachieum, but would also be 
found in other Trematoda. The first to be examined were of 
course other species of Diplostomum. Diplostomum volvens, 
and D. clavatum from the lens and vitreous humour of several 
fresh-water fishes, were examined, and afforded the expected 
results. The excretory system in these two species having 
been sufficiently described by Nordmann,* it is only neces- 
sary to remark in addition, that in them also the vessels 
terminate in globular dilatations and enclose the corpuscles. 
In the three species of Diplostomum examined, one particular 
part of the body was found especially adapted for the exhi- 
bition of the condition in question—the region, viz., behind 
the hindermost acetabulum. In this situation the corpuscles 
are only sparingly distributed, and the connexion between 
the cavities containing the corpuscles and the vessels is 
readily seen when the animal is quiescent. 
The calcareous corpuscles of the Diplostomata are thus in 
all respects similar to those which are found in the main 
trunks of the excretory system in many Cercarie and certain 
Distomata. 1 am unable therefore to agree with M. Moulinié+ 
in viewing the two kinds of corpuscles as distinct from each 
other. According to this author, the corpuscles which occur, 
as he thinks, not in the vascular system but in the paren- 
* ‘Micrograph. Beitrige zur Naturgesch. der Wirbellosen Thiere,’ 
p. 37 ef seq. 
+ ‘ De la reproduction chez les Trématodes endo-parasites.’ Genéve, 1816, 
p. 223 
